<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <p>回调函数等待 3 秒后执行。</p>
    <p id="demo1"></p>
    <p id="demo2"></p>
<script>
    setTimeout(() => {
        document.getElementById("demo1").innerHTML="RUNOOB-1";
    }, 3000);
    document.getElementById("demo2").innerHTML="RUNOOD-2"
</script>
</body>
</html>